The invention relates to a method for assembling electroconductive parts by electric current heating, a device for its implementation as well as its use.
Until now, electroconductive components, particularly hollow bodies, such as long, closed profiles or big, massive parts that are difficult for electrodes to contact from the underside could be assembled often only through thermal assembly with filler metal, soldering material, or the like.
A disadvantage of this thermal assembly method is that the heat needed for assembly cannot be placed precisely. The parts to be assembled are therefore heated up more than is necessary for the pure assembly process of welding or soldering, and the parts partially lose their dimensional accuracy, or the material suffers a disadvantageous structural deformation (for example, in work-hardened parts that originate from cold forming method, like the internal high-pressure metal forming method explained below in detail. In extreme cases, the preformed part to be assembled loses its shape and a part of its firmness.
Spot welding with laser picker or the like also has other disadvantages.
The internal high pressure process as such is known. Under the mentioned internal pressure method or even the internal high pressure method, the word method is understood as that which was described in the lndustrieanzeiger No. 20, dated Mar. 9, 1984 or even in the xe2x80x9cMetallumformtechnikxe2x80x9d, ID/91 edition, page 15 ff: A. Ebbinghaus: Aviation Type Precision Work Pieces, produced through internal high-pressure metal forming xe2x80x9cor Werkstoff und Betriebxe2x80x9d 123 to 243: A. Ebbinghaus: xe2x80x9cEconomic Construction with internal high-pressure metal formed Precision Piecesxe2x80x9d or xe2x80x9cWerkstoff und Betriebxe2x80x9d 122, (1991), 11, (1989), page 933 to 938. To avoid repetition, reference will subsequently be made to the disclosure of these publications in full. The method was previously used for the manufacture of hollow parts of various shapes, such as for the manufacture of constructed camshafts to fasten cams to a tube, for the manufacture of hollow camshafts, for the manufacture of steering axles, as well as for the manufacture of vehicle frame parts.
It delivers highly precise, cold-formed parts that have experienced a cold hardening during the shaping and whose fibre run, as determined in the course of a microscopic observation of the ground sections, essentially corresponds to the run of the outer contours of the shaped part. As a result, these parts are very sturdy or light in relation to their strength.
In order to avoid the disadvantageous heating up, particularly of such types of work-hardened whole parts, resistance welding could also be used because the current used there for welding heats up precisely between two or several electrodes, said electrodes of one polarity being called xe2x80x9cwelding electrodesxe2x80x9d and the electrodes of the opposite polarity being called counterelectrodes. One-sided indirect welding, in which a material with very good conductivity (counter copper1) is placed under the sheet metals to be assembled, has the disadvantage in that the welding current is prone to shifting, so that welding points are created at points totally different from the desired locations. Such as method for impulse welding, in which the welding electrodes are supplied from one side to the parts for assembly,
Furthermore, problems with the achievable welding deposits often occurred with large equipment, all the more the bigger the parts to be welded, the earlier the shunt wounds could occur.
It is therefore the task of the invention to create a method for assembling parts through resistance welding, which can also be used for parts that are easily accessible only from one side.
The task is solved according to the invention through a method for assembling electroconductive parts by heating by means of electric current, in which electrodes of different polarity are supplied from the same side of the parts to be assembled and touch at least one of the parts to be assembled, current is applied to the electrodes, and in such a manner, the conductive parts are heated and assembled through the current flowing from one electrode to the other through the parts to be assembled.
Advantageous developments are in the dependent claims.
To increase the welding deposits, a certain amount of force can be applied to the surfaces/parts to be assembled, thereby improving the electrically capable contact and allowing higher welding current to flow. In the process, the parts may fuse partially or completely in the heated up area, or welding material or solder may be placed for smelting.
As the expert in the field of electrical welding engineering knows, the electrodes can be cooled in a known manner. When superconductive materials, such as special ceramic, are used, the electrodes may of course be cooled appropriately through liquid helium or nitrogen.
The parts may also be assembled by using electroconductive soldering material between the parts, thereby involving a soldering procedure.
In the process, one may be surrounded by one or several counterelectrodes surrounding the same, or the counterelectrodes may enclose the central electrode in a ring shape, or two counterelectrodes, between which the central electrode is placed, may be used.
In cases where the underside of the parts for assembly is accessible, it may be advantageous to place under the electroconductive parts for assembly, on the surface of the compound arrangement opposite the electrodes, a counter material of greater electroconductive capacity than the parts for assembly, in order to improve the current passage through the parts for assembly.
If the parts for assembly exhibit differing electroconductivity, it is preferable to make the conductivity of the part, which is not in contact with the electrodes, higher than that of the part that is contacted by the electrodes.
It is useful to develop, in at least one of the parts for assembly, an opening for the penetration of an electrode and to make contact only with the object behind it so that through this electrode, a potential other than the one to be placed on the upper part can be placed on the lower part, so that current flows between the two, and if necessary, soldering material as well, and this is heated locally for welding/soldering. If the material thickness permits, it makes sense to perform the procedure in such a way that an opening for penetration of one electrode be made, for example, through drilling, stamping, cutting, or the like, before applying of the electrodes.
A device according to the invention for performing the procedure according to any one of the previous claims shows at least two adjacently arranged electrodes, which are insulated from one another and are movable from the same parts towards the parts for assembly; and a power supply for applying high voltage/intensity of current of varying potential to the electrodes of different polarity.
At the same time, this device may comprise a facility for creating openings suitable for the passage of internal electrodes and insulated against the contact with the opening walls.
It is useful for the device to also comprise during the assembly a device for exerting pressure on the electroconductive parts to be assembled because, with better contact between the two parts, the current can flow better through the same. This device may, for instance, be formed by one or several electrodes, but if the underside of the electroconductive parts to be assembled is accessible, it may also comprise the conductive counterpart (xe2x80x9ccopper back-up barxe2x80x9d), which then interacts with the electrodes.
The electrodes may be shaped in such a way that the counter electrode at least partially encloses the central electrode. Several counterelectrodes, which at least partially enclose a central electrode between them, may also be provided. There may be an insulation material between the electrodes of different polarity.
For instance, an electrode may be shaped as a hollow body, for example, as a hollow cylinder, in which the counterelectrode is axially movable, in such a way that it contacts, through an opening accessible in the upper part, an area of the lower part insulated from the upper part (for example, avoiding the upper part from being touched by the conductive electrode, or a contact taking place only with an electrically non-conductive outer casing of the electrode), and the other electrode contacts the part under it and such types of voltages of different potentials may be created between the two parts.
It is useful to have an insulation material between the electrodes, such as air, an insulating gas, or non-conductive and high-temperature-resistant synthetic material, such as Teflon as well as ceramic. It is preferred for this insulating material to insulate not only electrically, but also thermally, in order to treat the electrode material with care. For many applications, it is particularly advantageous for the inner electrode to be covered by insulation material except on the contact points, for example, a porcelain, synthetic, or other insulating shell, in which the electrode is movable, with the electrode contact being exposed.
It is advantageous if, in the device, a facility for the production of openings is provided, suitable for the passage of the inner electrodes and insulated against contact with the opening walls, said equipment being a drilling equipment, perforating equipment, or cutting equipment, which provides openings only for the upper part or also both parts, such openings providing access to the underlying part for contact with the counter electrode.
A preferred use of the device is the assembly of hollow parts, closed profiles or large and/or thick objects with sheet metal that fie partially flat. Thus, hollow bodies, closed profiles or massive parts can be assembled with sheet metal or other hollow parts. A typical application is the assembly of support parts in vehicle construction, which includes land, air and water vehicles, with sheet metal, a typical area of application being the connection between support parts of the underbody of an automobile with sheet metal, such as floor panels. However, hollow tubes may also be assembled with sheet metal, or the like, in aircraft construction. Corresponding applications are obvious to the expert.
On account of the extremely short current paths from one electrode, through the welding zone, to the other electrode, which the method according to the invention offers, it also seems suitable, in certain cases, where good access on both sides exist, to substitute the spotwelding with counterelectrode using the method according to the invention. Or there, where shunt wounds threaten as a result of too little welding spot distance, or where sheet metal with very different wall thicknesses are supposed to be welded. The risks of shunt wounds, which are a threat in so-called indirect welding (both electrodes on the same side, but not coaxial), are greatly reduced or completely eliminated with the method according to the invention.